- Alternative Character Interpretation:
- Amberley can be seen as enjoying Cain for his abilities and occasional company, but some lines make her look like a Clingy Jealous Girl, notably when she mentions she'd have found out if Cain was really trying to seduce women he met.
- Similarly, it is possible to interpret Cain's monogamy after getting involved with Amberley as simply his self-defense instincts kicking in: "When dating an Inquisitor, it ain't over till she says it's over!" (His comment about only having room in his life for one lethally dangerous woman comes to mind.)
- Cain is a Dirty Coward, a Lovable Coward, The So-Called Coward, or went through those steps along the way towards his retirement.
- Discredited Meme: For many fans, typing HERO OF THE IMPERIUM after every instance of Cain's name.
- Ensemble Dark Horse:
- Sergeant Rock Lustig and his Unluckily Lucky subordinate "Jinxie" Penlan.
- Sorel, the Cold Sniper from the first book.
- Reasonable Authority Figure General Zyvan.
- Mira, Cain's Girl of the Week in the seventh book, for managing to be both a humorous Upper-Class Twit and a decent Action Girl at the same time.
- Alaric Tayber- the efficient Perlia PDF official who helps kick start Cain's rescue of thousands of people- and Badass Bureaucrat Scrivener Norbert from Death or Glory.
- Alaric's sister Felicia Tayber appears to be very popular among fan artists, likely due to being the only canonically attractive tech priest in 40K.
- Kayla and Donal are considered the most notable of Cain's commissar cadets in the sixth book.
- Sister Julien, the Perlia Battle Sisters inspector made a surprisingly decent impression on fans.
- Amberly's....eccentric psyker Rakel has her fans.
- "Funny Aneurysm" Moment: If you read in continuity order; a Call-Forward in publication order. In Death or Glory, Jurgen is mostly uninjured by a blow to the head, and Cain says, "It would probably take a bolter shell to crack that thick skull of his." In For the Emperor, Jurgen's skull is fractured near-fatally by... a bolter shell that glances off his helmet.
- Genius Bonus: Overlaps a lot with the Shout Outs on the main page.
- Hilarious in Hindsight:
- In the novel "Caves of Ice," Cain makes reference to a myth going around that at the dawn of the forty-second millenium, the Emperor would get up off his throne and resume command of the Imperium. This was released in 2004. 13 years later, Eighth Edition has just been released and while the Emperor did not get off the Throne, His son, Roboute Guilliman, has.
- "Commissar Donal sends his regards."
- Pyrovores, mocked for their uselessness in The Last Ditch, as mentioned below, have been fixed in 8E by giving them better melee stats and making their explosions only hurt ENEMY models. Apparently, the hivemind has learned from that incident...
- Iron Woobie: Issues of self-esteem are the least of humanity's worries in the Warhammer 40K universe and so it's never emphasized in the books, but Cain has enough trust issues and paranoia to disturb Harry Dresden, and a self-esteem so low that it should be measured in the negative. He goes through his entire life convinced that no one could or should care for him personally, unable to connect with people on any meaningful level, unable to ever credit that he's a remotely decent person or so much as pat himself on the back for the billions of lives he saves, and terrified to trust anyone with his thoughts, lest he be shot for cowardice and deceit. The closest this ever gets to a Lampshade Hanging is when, at their second meeting, Amberley gently implies that she isn't fooled by his facade and suggests that he could try being himself. He practically shits his pants thinking that she's a psyker and is going to have him killed, and he never actually takes her into his confidence even after a century of romance. That's sad.
- Memetic Mutation: One of the few memes originating from TV Tropes: it has become tradition to write HERO OF THE IMPERIUM after Cain's name whenever he appears on another page.
- Squick: The Mechanicus genestealer-breeding experiments in The Greater Good (where convicts are implied to have been forcibly impregnated by infected test subjects) are squicky enough to visibly disturb a visiting Tau.
- Take That, Scrappy!: In The Last Ditch the Tyranids deploy a number of Pyrovores, a notoriously badly designed unit which is more likely to blow up itself (and a huge chunk of its allies) than anything useful. Cain exploits this fact by killing them when they're near the Hive Tyrant, and they end up winning the deciding battle of the war for the Imperium.
- They Wasted a Perfectly Good Plot: Fairly early in The Greater Good, Tau ambassador El'hassai suggests an exchange of observers between the allied Imperial and Tau forces and suggests Cain to be the human representative in the Tau fleet. Instead of agreeing and the book being about Cain fighting alongside the Tau, he nominates ambassador Donali to go instead and sticks with the Imperial force for the rest of the book. As a result, the scene on the cover of Cai back-to-back with a Fire Warrior facing down a swarm of Tyranids never happens and the Tau go on to play almost no part in the rest of the story.
YMMV / Ciaphas Cain